I am sure, the below links will be useful for your apex learning process.

http://www.inside-oracle-apex.com/oracle-apex-4-0-early-adopter-blog-coverage/

• APEX 4.0: Tree View vs Component View by Dimitri Gielis
• [Oracle APEX 4.0] Search application by Whitehorses
• APEX 4.0: writing higher quality applications by using the Advisor by Dimitri Gielis
• APEX 4.0 – First Impressions by John Scott
• [Oracle APEX 4.0] Team Development by Whitehorses
• APEX 4.0: My thoughts after first round of playing by Dimitri Gielis
• Apex 4.0 Early Adopter – first shot by Stew Stryker
• [Oracle APEX 4.0] Application Translations by Whitehorses
• APEX 4.0 Web Services Evaluation Guide by Jason Straub

Plug-ins

• APEX 4.0: My first Plugin – Editable Select List / Combobox by Dimitri Gielis
• APEX 4.0 EA1 Plugins – Google Feed by Louis-Guillaume Carrier-Bédard
• APEX 4.0 EA1 Plugins – Google Visualization: Organizational Chart by by Louis-Guillaume Carrier-Bédard
• APEX 4.0 EA1 Plugins – jQuery UI Tabs by Louis-Guillaume Carrier-Bédard
• Creating plugin item types using APEX 4.0 by Whitehorses
• Oracle APEX 4.0, Plugins and a happy new Year by Peter Raganitsch